#include <vector>

using namespace std;

struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode() : val(0), left(nullptr), right(nullptr) {}
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
    TreeNode(int x, TreeNode* left, TreeNode* right) : val(x), left(left), right(right) {}
};

class Solution {
public:
    void inorder(vector<int>& res, TreeNode* root) {
        if (root == nullptr) {
            return;
        }
        inorder(res, root->left);
        res.push_back(root->val);
        inorder(res, root->right);
    }

    vector<int> inorderTraversal(TreeNode* root) {
        vector<int> res;
        inorder(res, root);
        return res;
    }
};

int main() {
    return 0;
}